Journal of Orthopaedic & Sports Physical Therapy    Official Publication of the Orthopaedic and Sports Physical Therapy Se...
There are numerous exercises used for abdominalstrengthening. Many of these exercises also activateextraneous (nonabdomina...
The purpose of this study was to test the effective-ness of 7 popular commercial abdominal machinesand 2 common abdominal ...
bent-knee sit-up (Figure 8) and crunch (Figure 9).No subject had prior experience in performing the 7commercial abdominal ...
Procedures                                                         subject’s right side (except for the internal oblique, ...
a slow and controlled manner using the 3-second             and expressed as a percentage of a subject’s highestcadence pr...
TABLE 1. Average EMG (±SD) for each muscle and exercise expressed as a % of maximum isometric voluntary contraction.      ...
100                                              90                                              80                   Norm...
70                                60     Normalized EMG (%MVIC)                                50                         ...
exercises activated abdominal musculature by actively                 anterior fibers of the intervertebral disk are com-f...
Biomechanical Differences Between the Crunch and                   Technique VariationsBent-Knee Sit-up                   ...
Paper 01 emg abdominal escamilla feb 2006
Paper 01 emg abdominal escamilla feb 2006
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Paper 01 emg abdominal escamilla feb 2006

  1. 1. Journal of Orthopaedic & Sports Physical Therapy Official Publication of the Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy AssociationAn Electromyographic Analysis ofCommercial and Common AbdominalExercises: Implications for Rehabilitationand TrainingRafael F. Escamilla, PT, PhD, CSCS 1Michael S.C. McTaggart, MS 2Ethan J. Fricklas, MSE 3Ryan DeWitt, MPT 4Peter Kelleher, MPT 4Marcus K.Taylor, PhD 5 RESEARCHAlan Hreljac, PhD 6Claude T. Moorman, III, MD 7Study Design: A repeated-measures, counterbalanced design. Conclusions: The Ab Slide and Torso TrackObjectives: To test the effectiveness of 7 commercial abdominal machines (Ab Slide, Ab Twister, were the most effective exercises in activating REPORTAb Rocker, Ab Roller, Ab Doer, Torso Track, SAM) and 2 common abdominal exercises (crunch, abdominal and upper extremity muscles whilebent-knee sit-up) on activating abdominal and extraneous (nonabdominal) musculature. minimizing low back and rectus femoris (hipBackground: Numerous abdominal machine exercises are believed to be effective in activating flexion) activity. The Ab Doer, Ab Twister, Ababdominal musculature and minimizing low back stress, but there are minimal data to substantiate Rocker, SAM, and bent-knee sit-up may bethese claims. Many of these exercises also activate nonabdominal musculature, which may or may problematic for individuals with low back pa-not be beneficial. thologies due to relatively high rectus femorisMethods and Measures: A convenience sample of 14 subjects performed 5 repetitions for each activity. J Orthop Sports Phys Ther 2006;36:45-exercise. Electromyographic (EMG) data were recorded for upper and lower rectus abdominis, 57.external and internal oblique, pectoralis major, triceps brachii, latissimus dorsi, lumbarparaspinals, and rectus femoris, and then normalized by maximum muscle contractions. Key words: EMG, low back pain,Results: Upper and lower rectus abdominis EMG activities were greatest for the Ab Slide, Torso lumbar spine, rectus abdominis,Track, crunch, and Ab Roller, while external and internal oblique EMG activities were greatest for sit-upthe Ab Slide, Torso Track, crunch, and bent-knee sit-up. Pectoralis major, triceps brachii, andlatissimus dorsi EMG activities were greatest for the Ab Slide and Torso Track. Lumbar paraspinalEMG activities were greatest for the Ab Doer, while rectus femoris EMG activities were greatest for Sthe bent-knee sit-up, SAM, Ab Twister, Ab Rocker, and Ab Doer. trong abdominals are im- portant for stabilizing1 the trunk and helping Associate Professor of Physical Therapy, California State University Sacramento, Sacramento, CA.2 Graduate student (at the time of study), Duke University Medical Center, Durham, NC. unload stress in the lum-3 Student (at the time of study), Duke University Medical Center, Durham, NC. bar spine.3,13 Abdominal4 Student (at the time of study), California State University Sacramento, Sacramento, CA. muscles (rectus abdominis, exter-5 Lieutenant, Medical Service Corps, US Navy, Naval Health Research Center, San Diego, CA.6 Associate Professor of Kinesiology and Health Science, California State University Sacromento, nal oblique, internal oblique, andSacromento, CA. transverse abdominal) are com-7 Associate Professor of Orthopaedic Surgery, Duke University Medical Center, Durham, NC. monly strengthened by activelyThe protocol used in this study was approved by the Institutional Review Board at Duke UniversityMedical Center, Durham, NC. The authors of this manuscript affirm we have no financial affiliation flexing the trunk with a concentric(including research funding) or involvement with any commercial organization that has a direct financial muscle action or by resisting trunkinterest in any matter included in this manuscript. extension (due to an externalAddress correspondence to Rafael Escamilla, Associate Professor of Physical Therapy, California StateUniversity Sacramento, Department of Physical Therapy, 6000 J Street, Sacramento, CA 95819-6020. force such as gravity) with an iso-E-mail: rescamil@csus.edu metric or eccentric muscle action.Journal of Orthopaedic & Sports Physical Therapy 45
  2. 2. There are numerous exercises used for abdominalstrengthening. Many of these exercises also activateextraneous (nonabdominal) muscles, such as the hipflexors, lumbar paraspinals, or upper extremity mus-culature, which may or may not be beneficial. Forexample, high activation levels from the hip flexorsand lumbar paraspinals tend to generate a forcecouple that attempts to anteriorly rotate the pelvisand increase lumbar lordosis. When coupled withweak abdominal musculature, activation of these ex-traneous muscles may increase the risk of low backpathologies. Understanding the muscle activation generated bydifferent abdominal exercises is useful to therapistsand other health care or fitness specialists whodevelop specific abdominal exercises for their pa-tients or clients to facilitate their rehabilitation ortraining needs and objectives. For example, abdomi-nal exercises that actively flex the trunk may beproblematic for individuals with lumbar disk patholo-gies due to increased intradiscal pressure18 and lum-bar spine compression,3 and for individuals with FIGURE 1. Ab Rocker.osteoporosis due to the risk of vertebral compressionfractures.21 However, these same individuals may beasymptomatic during abdominal exercises that main-tain a relatively neutral spine and pelvis. In contrast,individuals with facet joint syndrome, spondylolis-thesis, and vertebral or intervertebral foramenstenosis may not tolerate exercises such as the AbSlide and Torso Track due to the extended spineposition. There are numerous commercially available ab-dominal machines that are believed to be effective inactivating abdominal musculature and minimizinglow back stress, but there are little or no scientificresearch data to substantiate these beliefs. Whilethere are numerous studies that examined muscleactivity during more traditional abdominal exercises,such as the sit-up or crunch exercises,3,14,16,26,27 thereis a scarcity of data related to the use of abdominalmachines. A limited number of studies comparedselect abdominal muscle activity while performingexercises using the Torso Track, Ab Doer, Ab Shaper,Ab Flex, and Ab Roller,6,7,12,24,26 but there are nostudies that we are aware of that have quantifiedabdominal muscle activity while using the Ab Twister,Ab Rocker, Super Abdominal Machine (SAM), andAb Slide. Moreover, when using abdominal machines,the extent of recruitment of extraneous musculature, FIGURE 2. Ab Roller.such as low back or upper and lower extremitymusculature, is currently unknown because there nal machines allow only uniplanar motions, such ashave been no studies that have reported extraneous trunk flexion, while others use multiplanar motions,muscle activity while performing these exercises. It is such as trunk flexion and rotation. It is commonlyalso unknown how abdominal machines compare to believed that performing simultaneous trunk flexiontraditional abdominal exercises, such as the sit-up and and rotation recruits the external and internal ob-crunch, in recruiting the abdominal musculature. lique musculature to a greater extent compared to Abdominal machines use various techniques to trunk flexion only. However, there is currently notarget different muscles. For example, some abdomi- scientific evidence to support this assertion.46 J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006
  3. 3. The purpose of this study was to test the effective-ness of 7 popular commercial abdominal machinesand 2 common abdominal strengthening exercises onactivating abdominal and extraneous musculature. Itwas hypothesized that significant differences would befound in the normalized electromyographic (EMG)data of both abdominal and extraneous muscle activ-ity among exercises.METHODSSubjects To optimize the EMG signal, this study was limitedto a convenience sample of 14 healthy, young subjects(7 male and 7 female) who had normal or belownormal amounts of body fat for their age group.Baseline skinfold calipers (model 68900; CountryTechnology, Inc, Gays Mill, WI) and appropriateregression equations were used to assess percent bodyfat, and standards set by the American College ofSports Medicine were used to determine normal or FIGURE 4. Ab Twister.below normal amounts of body fat.4 Mean (±SD) age, RESEARCHmass, height, and percent body fat were 24.1 ± 5.4years, 58.7 ± 4.9 kg, 166.8 ± 5.9 cm, and 22.7% ±1.9%, respectively, for females, and 24.0 ± 7.1 years,78.6 ± 13.9 kg, 179.8 ± 4.1 cm, and 9.7% ± 4.1%,respectively, for males. All subjects provided writteninformed consent in accordance with the InstitutionalReview Board at Duke University Medical Center. REPORT FIGURE 5. Torso Track. FIGURE 6. Ab Slide. Individuals were excluded from the study if they had a history of abdominal or back pain, or were unable to perform all exercises pain free and with proper form and technique for 12 consecutive repetitions. Exercise Descriptions The 7 abdominal machine exercises were the Ab Rocker (Figure 1), Ab Roller (Figure 2), Ab Doer (Figure 3), Ab Twister (Figure 4), Torso Track (Figure 5), Ab Slide (Figure 6), and SAM (Figure 7).FIGURE 3. Ab Doer. The 2 common abdominal exercises tested were theJ Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006 47
  4. 4. bent-knee sit-up (Figure 8) and crunch (Figure 9).No subject had prior experience in performing the 7commercial abdominal exercises, but they had mod-erate experience in performing the crunch andbent-knee sit-up. The Ab Rocker, Ab Twister, Ab Doer, and SAMexercises started and ended in a seated position witha neutral spine and pelvis. The 2 common move-ments advertised for the Ab Rocker and Ab Twisterwere the crunch (involving sagittal plane trunk flex-ion) and the oblique crunch (moving obliquelyacross the body by simultaneously flexing and rotat-ing the trunk), and both were tested with rotationoccurring to the left. Three common movementsadvertised for the Ab Doer were the body bob FIGURE 8. Bent-knee sit-up.(frontal plane side-to-side motion), body boogie(moving in a circular motion), and good morning(involving sagittal plane trunk flexion), and all 3 ofthese variations were tested. The movement for theSAM involved sagittal plane trunk flexion, similar tohow the Ab Rocker (crunch), Ab Twister (crunch),and Ab Doer (good morning) were performed. The Ab Roller, crunch, and bent-knee sit-up startedand ended in a supine position. The crunch and AbRoller both had 2 variations: a normal crunch involv-ing sagittal plane trunk flexion and an obliquecrunch involving moving obliquely across the body by FIGURE 9. Crunch. simultaneously flexing and rotating the trunk to the left. The primary differences between the 2 exercises were that during the Ab Roller the head was sup- ported by a head pad and the arms were supported by a supporting bar (Figure 2), while during the crunch the thumbs were positioned in the ears and the hands were relaxed against the head (this hand position was standardized for comfort for both the crunch and bent-knee sit-up) (Figure 9). Both varia- tions for the crunch and Ab Roller involved a curling-up motion (trunk flexion or trunk flexion with left rotation) until both scapulae were off the ground. During the bent-knee sit-up the thumbs were positioned in the ears with the hands relaxed against the head, the feet were supported and held down, the knees were flexed approximately 90°, and from this supine position the subject simultaneously flexed the trunk and hips until the elbows were even with the knees (Figure 8). The Ab Slide and Torso Track started and ended in the quadruped position (on hands and knees with hips and shoulders flexed approximately 90°), with a neutral spine and pelvis. From this position the subject straightened out the body by rolling forward in a straight line (Torso Track and Ab Slide straight) or a curved line to the left (Ab Slide curved), while maintaining a neutral spine and pelvis (Figures 5 andFIGURE 7. SAM. 6).48 J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006
  5. 5. Procedures subject’s right side (except for the internal oblique, which was positioned on the subject’s left side) for All subjects became familiar with all abdominal the following muscles in accordance with proceduresexercises during a pretest session that took place previously described 5,8,17,20 : (a) upper rectusapproximately 1 week prior to the testing session. abdominis, positioned vertically and centered on theDuring the pretest session, each subject received muscle belly (not on tendinous intersection) near theinstructions explaining how to correctly perform midpoint between umbilicus and xiphoid process andeach of the abdominal exercises (each abdominal 3 cm lateral from midline; (b) lower rectusmachine came with written or video instructions for abdominis, positioned 8° from vertical inits use). All exercises were performed with a 3-second inferomedial direction and centered on the musclecadence (1 second from start of exercise to end belly near the midpoint between umbilicus and pubicrange, 1-second isometric hold at end range, symphysis and 3 cm lateral from midline; (c) external1-second return to starting position) and a 1-second oblique, positioned obliquely approximately 45° (par-rest between repetitions. The subjects practiced all allel to a line connecting the most inferior point ofexercises under the supervision of trained research the costal margin of the ribs and the contralateralpersonnel. All of the commercial exercises except the pubic tubercle) above anterior superior iliac spineAb Roller and Ab Slide had adjustable elastic bands (ASIS) near the level of the umbilicus; (d) internalto make the exercise easier or harder. To better oblique, positioned horizontally 2 cm inferomedial tonormalize the intensity of each exercise, resistance the ASIS, within a triangle confined by the inguinalwas adjusted according to each subject’s preference ligament, lateral border of the rectus sheath, and aand the manufacturer’s recommendation (eg, using a line connecting the ASISs (it has been demonstratedresistance that was not too hard but hard enough to that in this region only the aponeurosis of theallow the execution of at least 15 repetitions)— external oblique, and not the external oblique RESEARCHsimilar to how each subject would adjust the resis- muscle, covers the internal oblique)20; (e) sternaltance and use the equipment if they purchased it for pectoralis major, positioned horizontally 2 cm medialhome use. The selected resistance during the pretest to the axillary fold; (f) triceps brachii long head,session was also used for that subject during the positioned vertically over the long head muscle bellytesting session. For each exercise, each subject used a near midline of the arm approximately halfway be-resistance that enabled the subject to correctly per- tween the acromion and olecranon; (g) latissimusform at least 15 consecutive repetitions using the dorsi, positioned obliquely (approximately 25° from REPORT3-second cadence described above. It was not possible horizontal in an inferomedial direction) 4 cm belowto normalize all exercises with exactly the same inferior angle of the scapula; (h) rectus femoris,relative intensity because the Ab Roller, Ab Slide, positioned vertically near midline of thigh approxi-crunch, and bent-knee sit-up used the body only as mately halfway between ASIS and proximal patella;an external resistance, while the remaining exercises and (i) lumbar paraspinals, positioned vertically 3 cmused resistance bands in addition to body as external lateral to spine and near level of iliac crest betweenresistance. In addition, even when the maximum L3 and L4 vertebrae. A ground (reference) electroderesistance possible was used for the Ab Doer, Ab was positioned over the skin of the right acromionTwister, and Ab Rocker, all subjects indicated that process. Electrode cables were connected to thethey were capable of performing these exercises with electrodes and taped to skin appropriately to mini-more resistance. A metronome (set at 1 beat per mize pull on the electrodes and movement of thesecond) was used to help ensure proper cadence cables.both during the pretest and testing sessions. Once a Once the electrodes were positioned, the subjectsubject was able to correctly perform each exercise warmed up and practiced the exercises as needed,with the proper cadence, a testing session was sched- then data collection commenced. EMG data wereuled. collected using a Noraxon 16-channel telemyo EMG Neuroline (Medicotest Marketing, Inc, Ballwin, unit (Noraxon USA, Inc, Scottsdale, AZ), and theMO) disposable surface electrodes (type 720-00-S) amplifier bandwidth frequency was 10 to 500 Hz. Thewere used to collect EMG data. These oval-shaped input impedance of the amplifier was 20 000 k andelectrodes (22 mm wide and 30 mm long) were the common-mode rejection ratio was 130 dB. EMGplaced in a bipolar electrode configuration along the data were sampled at 1000 Hz, recorded by alongitudinal axis of each muscle, with a center-to- transmitter and amplifier, and broadcast to a receivercenter distance of approximately 3 cm between elec- interfaced to a computer. The recorded signals weretrodes. Prior to positioning the electrodes over each processed through an analog-to-digital (A/D) con-muscle, the skin was prepared by shaving, abrading, verter by a 16-bit A/D board.and cleaning with isopropyl alcohol wipes to reduce EMG data were collected during 5 repetitions forskin impedance values, which typically were less than each exercise, with all exercises performed in a10 k . Electrode pairs were then placed on the randomized order. Each repetition was performed inJ Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006 49
  6. 6. a slow and controlled manner using the 3-second and expressed as a percentage of a subject’s highestcadence previously described and 1-second rest be- corresponding MVIC trial, which was determined bytween repetitions. With a relatively low number of calculating throughout the 5-second MVIC the high-repetitions performed, all subjects acknowledged that est average EMG signal over a 1-second time interval.fatigue was minimized. Each testing session took Normalized EMG data were then averaged over the 5approximately 45 minutes to complete. repetition trials performed for each exercise and Randomly interspersed within the exercise testing used in statistical analyses.session, EMG data from each muscle tested werecollected during two 5-second maximum voluntary Data Analysisisometric contractions (MVICs). After conducting pi-lot work, we adopted the following protocols for A 1-factor repeated-measures analysis of varianceMVIC testing, which were based on the positions that was employed to assess differences in normalizedelicited the greatest MVIC for each respective muscle EMG muscle activity among the different exercise(all MVICs were collected on a plinth with subject in variations (P .01). Post hoc analyses were performeda prone, supine, or short-sitting position): (a) upper using the Bonferroni test to evaluate the significanceand lower rectus abdominis, body supine with hips of between-exercise pairwise comparisons (P .01).and knees flexed 90°, feet supported, and trunkmaximally flexed (ie, curl-up position), with resis-tance at the shoulders in the trunk extension direc- RESULTStion; (b) external and internal oblique, body supine Normalized EMG data for each muscle and exer-with hips and knees flexed 90°, feet supported, and cise are shown in Table 1. Among all exercises tested,trunk maximally flexed and rotated to the left, with upper rectus abdominis EMG activities were greatestresistance at the shoulders in the trunk extension for the Ab Slide (straight and curved), Torso Track,and right rotation directions; (c) sternal pectoralis crunch (normal and oblique), and Ab Roller (crunchmajor, body supine with right shoulder flexed 90° and oblique) exercises, and lowest for the Ab Twisterand internally rotated, the right forearm supinated, (crunch and oblique), Ab Rocker (crunch and ob-and the right elbow slightly flexed, with resistance at lique), and Ab Doer (good morning, body boogie,the right distal arm and forearm in the horizontal and body bob) exercises. Lower rectus abdominisabduction direction; (d) triceps long head, body EMG activities were greatest for the Ab Slide (straightprone with right shoulder abducted 90° and right and curved) and Torso Track exercises, and lowestelbow flexed 45°, with resistance at the right distal for the Ab Twister (crunch and oblique), Ab Rockerforearm in the elbow flexion direction; (e) latissimus (crunch and oblique), and Ab Doer (good morning,dorsi, body prone with right shoulder abducted 0° body boogie, and body bob) exercises. Graphicaland extended maximally, with resistance at the right representations of upper and lower rectus abdominisdistal arm in the direction of shoulder flexion; (f) activity ranked from highest to lowest among alllumbar paraspinals, body prone with trunk fully exercises are shown in Figures 10 and 11.extended and hands clasped behind head, with resis- The external oblique EMG activity for the crunchtance at the shoulders in the direction of trunk (normal), Ab Roller (crunch), and Ab Doer (goodflexion; and (g) rectus femoris, body in short-sitting morning) exercises were significantly lower comparedposition with hips and knees flexed 90°, with resis- to the Ab Slide (straight and curved) and bent-kneetance at the distal leg in the knee flexion direction. sit-up exercises. Internal oblique EMG activities wereThe MVICs were collected to normalize the EMG greatest for the Ab Slide (straight and curved), Torsodata collected during the abdominal exercises. Each Track, bent-knee sit-up, and crunch (normal andsubject was given similar verbal encouragement for oblique) exercises, and lowest for the Ab Rollereach MVIC to help ensure a maximum effort (oblique), Ab Twister (crunch and oblique), Abthroughout the 5-second duration, and the subject Rocker (crunch and oblique), and Ab Doer (goodwas asked after each MVIC if he/she felt it was a morning) exercises. Graphical representation of ex-maximum effort. If not, the MVIC was repeated. An ternal and internal oblique activity ranked fromapproximately 1-minute rest was given between each highest to lowest among all exercises are shown inMVIC and an approximately 2-minute rest was given Figures 12 and 13.between each exercise trial. Sternal pectoralis major EMG activities were great- est for the Ab Slide (straight and curved), TorsoData Processing Track, SAM, and Ab Twister (crunch and oblique) Raw EMG signals were full-wave rectified, smoothed exercises, and lowest for the Ab Rocker (crunch andwith a 10-millisecond moving average window, and oblique), Ab Doer (good morning, body boogie, andlinear enveloped, then averaged over the entire body bob), Ab Roller (crunch and oblique), andduration of each exercise repetition. For each repeti- crunch (normal and oblique) exercises. Tricepstion the EMG data were normalized for each muscle brachii long head EMG activities were significantly50 J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006
  7. 7. TABLE 1. Average EMG (±SD) for each muscle and exercise expressed as a % of maximum isometric voluntary contraction. Sternal Upper Rectus Lower Rectus External Internal Pectoralis Triceps Latissimus Lumbar Rectus Abdominis* Abdominis* Oblique* Oblique* Major* Long Head* Dorsi* Paraspinals* Femoris* Ab Slide (straight) 67 ± 26 72 ± 19 40 ± 16 53 ± 15 23 ± 7 30 ± 12 10 ± 4 3 ± 2k 5 ± 3fhj Ab Slide (curved) 61 ± 24 66 ± 19 42 ± 17 51 ± 15 20 ± 9 26 ± 12 10 ± 3 2 ± 2k 9 ± 7f Torso Track 67 ± 25 72 ± 17 32 ± 18 58 ± 14 20 ± 8 26 ± 11 10 ± 5 2 ± 2k 6 ± 5fhj Crunch (normal) 51 ± 9 50 ± 8ab 16 ± 11af 41 ± 9 4 ± 3abgi 1 ± 1ab 5 ± 1g 2 ± 1k 3 ± 2fhj Crunch (oblique) 50 ± 15 39 ± 14ab 32 ± 22 40 ± 11 6 ± 5agi 2 ± 2ab 8±5 5 ± 3k 3 ± 2fhj Bent knee sit-up 38 ± 12ab 44 ± 13ab 41 ± 16 49 ± 21 8 ± 6ag 2 ± 2ab 6 ± 3g 4 ± 2k 36 ± 16 SAM 42 ± 17ab 50 ± 20ab 31 ± 21 36 ± 13b 26 ± 15 10 ± 6ab 12 ± 6 4 ± 2k 20 ± 15 Ab Roller (crunch) 46 ± 17 42 ± 12ab 13 ± 8af 38 ± 9b 7 ± 5agi 3 ± 2ab 5 ± 2g 3 ± 2k 1 ± 1fhj Ab Roller (oblique) 49 ± 12 36 ± 16ab 20 ± 9 25 ± 11abf 5 ± 3abgi 3 ± 2ab 6 ± 2g 3 ± 2k 2 ± 2fhj Ab Twister (crunch) 19 ± 8abcde 19 ± 10abcdefg 21 ± 12 22 ± 9abf 13 ± 11 7 ± 3ab 5 ± 2g 4 ± 3k 27 ± 19 Ab Twister (oblique) 20 ± 7abcde 22 ± 11abcfg 33 ± 18 28 ± 11abf 22 ± 15 5 ± 4ab 6 ± 2g 5 ± 6k 24 ± 14 Ab Rocker (crunch) 15 ± 8abcdefg 13 ± 5abcdefg 22 ± 11 24 ± 8abf 7 ± 7agi 6 ± 4ab 6 ± 3g 4 ± 3k 30 ± 21 Ab Rocker (oblique) 14 ± 10abcdefg 14 ± 8abcdefg 31 ± 18 23 ± 8abf 6 ± 6agi 7 ± 4ab 5 ± 2g 3 ± 1k 21 ± 16 Ab Doer (good morning) 14 ± 7abcdefg 14 ± 5abcdefg 16 ± 11af 22 ± 13abf 4 ± 4abgi 2 ± 1ab 2 ± 2abg 15 ± 7 12 ± 11f Ab Doer (body boogie) 12 ± 4abcdefg 11 ± 6abcdefg 24 ± 10 31 ± 13b 3 ± 2abgi 1 ± 1ab 2 ± 1abg 13 ± 8 24 ± 19 Ab Doer (body bob) 7 ± 5abcdefg 7 ± 4abcdefg 30 ± 19 37 ± 18b 2 ± 2abgi 2 ± 1ab 1 ± 1abg 8±3 16 ± 14f * Significant difference (P .001) in EMG activity among abdominal exercises based on a 1-way repeated-measures analysis of variance. Key to pairwise comparisons (P .01):J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006 a. Significantly less EMG activity compared to the Ab Slide (straight and curved). b. Significantly less EMG activity compared to the Torso Track. c. Significantly less EMG activity compared to the crunch (normal). d. Significantly less EMG activity compared to the crunch (oblique). e. Significantly less EMG activity compared to the Ab Roller (crunch and oblique). f. Significantly less EMG activity compared to the bent-knee sit-up. g. Significantly less EMG activity compared to the SAM. h. Significantly less EMG activity compared to the Ab Twister (crunch). i. Significantly less EMG activity compared to the Ab Twister (oblique). j. Significantly less EMG activity compared to the Ab Rocker (crunch). k. Significantly less EMG activity compared to the Ab Doer (good morning and body boogie).51 REPORT RESEARCH
  8. 8. 100 90 80 Normalized EMG (%MVIC) 70 60 50 40 30 20 10 0 M ) ck b) ) ) ) ) ) ) t) ) p ) ) ed ) ch ch ue ch ie ue ue ue al SA ng t-u gh bo a og m rv un un un liq Tr liq liq iq ni i si ra or u dy bo bl or cr ob ob cr ob cr (c o e t (n (o (s rs r( bo m r( r( ne r( r( r( dy e To ch ke h te e le id r( od -k te le ke bo nc id ol Sl is n oc nt ol oe is go Sl oc ru r( Tw R ru Tw R Be Ab R D r( C R oe C Ab Ab Ab Ab Ab Ab oe Ab Ab D D Ab AbFIGURE 10. Upper rectus abdominis normalized mean (SD) EMG activity among exercises. 100 90 80 Normalized EMG (%MVIC) 70 60 50 40 30 20 10 0 M ) b) ) ) ) p ) k d) ) ) ) ) ) ) ie ue ue ch ht ue ng ch ue al ch ac t-u SA bo ve og m ig un un un liq liq liq ni iq Tr si tra ur or bo or bl dy ob ob ob cr cr cr e o (c (n (o (s m ne bo r( rs r( r( r( r( r( dy e h To h e od te le ke -k r( te id le ke nc bo nc id ol is nt ol Sl is go oe oc Sl oc ru r( ru Tw R R Tw Be R Ab r( D C R C oeAb Ab Ab oe Ab Ab Ab Ab Ab D D Ab AbFIGURE 11. Lower rectus abdominis normalized mean (SD) EMG activity among exercises.greater for the Ab Slide (straight and curved) and boogie, and body bob) exercises compared to allTorso Track exercises compared to all other exercises. other exercises. Rectus femoris EMG activities wereLatissimus dorsi EMG activities were greatest for the greatest for the bent-knee sit-up, SAM, Ab TwisterAb Slide (straight and curved), Torso Track, SAM, (crunch and oblique), Ab Rocker (crunch and ob-crunch (oblique), and Ab Twister (oblique) exercises, lique), and Ab Doer (body boogie) exercises, andand lowest for the Ab Doer (good morning, body lowest for the Ab Roller (crunch and oblique), Abboogie, and body bob) and Ab Roller (crunch) Slide (straight), Torso Track, and crunch (normalexercises. and oblique) exercises. The relative effectiveness of Lumbar paraspinal EMG activities were significantly exercises in muscle recruitment of the trunk, uppergreater for the Ab Doer (good morning, body extremity, and hip musculature is shown in Table 2.52 J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006
  9. 9. 70 60 Normalized EMG (%MVIC) 50 40 30 20 10 0 ) M b) ) d) ) ) ) ) ) ) ) k p ) ) al ht ie ue ue ng ch ue ue ch ch ac t-u SA bo ve m og ig un un un liq iq ni liq liq Tr si or ur tra bo bl or dy ob ob ob cr cr cr e o (n (c (o (s m ne bo r( rs r( r( r( r( r( dy e h h To e od le te ke -k r( id te le ke nc bo nc id ol is nt Sl ol is go oc oe Sl oc ru r( ru R Tw Tw R Be RAb r( C D R C Ab oe Ab Ab oe Ab Ab Ab Ab Ab D D Ab AbFIGURE 12. External oblique normalized mean (SD) EMG activity among exercises. RESEARCH 80 70 Normalized EMG (%MVIC) 60 50 40 REPORT 30 20 10 0 ) ) b) ) M d) ) ) ) p ) ) ) ) ) k ie ue ht ue ue ch ue ng ch al ch ac t-u SA bo ve og ig m un liq un un iq liq ni iq Tr si ur tra or bo bl bl or dy ob ob cr cr cr e (c o (n (o (o (s m ne Ab (bo r( r( r( rs r( r( dy e h h Ab ker e od To le te ke -k le id te nc bo nc id r ol is nt ol Sl is go oe oc Sl oc ru r( ru R Tw R Tw BeAb R r( D C R C oe Ab Ab oe Ab Ab Ab Ab D D Ab AbFIGURE 13. Internal oblique normalized mean (SD) EMG activity among exercises.DISCUSSION out’’ portion in performing the Ab Slide and Torso Track, the abdominal musculature contracts eccentri-Biomechanical Differences Between Flexion and cally or isometrically to resist the attempt of gravity to extend the trunk and rotate the pelvis. During theExtension Exercises return motion, the abdominal musculature contracts The Ab Slide and Torso Track were the most concentrically or isometrically. If the pelvis and spineeffective exercises in activating abdominal muscula- are stabilized and maintained in a neutral positionture, including the upper and lower rectus abdominis throughout the roll-out and return movements, thenand the external and internal oblique. While per- the abdominal musculature primarily would contractforming these exercises, the abdominal muscles con- isometrically. While performing these exercises, atract in a different manner compared to performing relatively neutral pelvis and spine were maintainedtraditional trunk flexion exercises. During the ‘‘roll- throughout the movement. In contrast, all otherJ Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006 53
  10. 10. exercises activated abdominal musculature by actively anterior fibers of the intervertebral disk are com-flexing the trunk by concentric contractions during pressed, while the posterior fibers are in tension. Inthe initial portion of the motion, an isometric con- addition, in extreme lumbar flexion intradiscal pres-traction during the middle portion, and an eccentric sure may increase several times above the normalcontraction during the final portion of the motion. intradiscal pressure from a resting supine posi- Understanding biomechanical differences between tion.18,19 While these stresses on the disk may not beexercises is important because trunk flexion may be problematic for the normal healthy disk, they may becontraindicated in certain populations, such as those detrimental to the degenerative disk or pathologicwith lumbar disk pathologies or osteoporosis. Main- spine.taining a neutral pelvis and spine (such as perform- There have only been a few studies that haveing the Ab Slide or Torso Track exercise), rather compared abdominal machine exercises to the tradi-than forceful flexion of the lumbar spine (such as tional crunch or bent-knee sit-up exercises.6,7,12,24,26during the bent-knee sit-up), may be desirable for Most of these studies compared the crunch to the Abthese individuals. In contrast, an individual with facet Roller, and like the results of the current study, therejoint pain, spondylolisthesis, and vertebral or were generally no significant differences in abdomi-intervertebral foramen stenosis may not benefit from nal muscle activity between these 2 exercises. Theexercises that maintain the spine and pelvis in a biggest difference between these exercises is that theneutral or extended position, such as when using the Ab Roller provides head support, which may make itAb Slide and Torso Track. These exercises may in fact more comfortable to perform compared to thecontribute to the nerve compression. However, trunk crunch. The only known study to investigate abdomi-flexion exercises, such as the crunch, bent-knee nal muscle activity between the crunch and the Torsosit-up, SAM, Ab Roller, Ab Twister, Ab Rocker, and Ab Track and Ab Doer (good morning) was by SternlichtDoer may be beneficial. and Rugg,24 and these authors found similar results When the lumbar spine is forcefully flexed, which as the current study: that abdominal muscle activitymay occur when performing many of the commercial was significantly greater in the crunch and Torsoabdominal machines used in the current study, the Track compared to the Ab Doer (good morning). TABLE 2. Relative muscle recruitment of the trunk, upper extremity, and hip musculature. Note: the Ab Slide (straight and curved) and Torso Track were the exercises that produced the greatest activation of the abdominal, oblique, and upper extremity musculature, while only minimally recruiting the hip flexors. Abdominal and Upper Extremity Oblique Muscles Muscles Low Back Muscles Hip Flexor Muscles Greatest recruitment • Ab Slide (straight and • Ab Slide (straight and • Ab Doer (good morn- • Bent knee sit-up curved) curved) ing and body boogie) • Ab Rocker (crunch) • Torso Track • Torso Track • Ab Twister (crunch) • SAM • Ab Doer (body boogie) • Ab Twister (oblique) Intermediate recruitment • Crunch (normal and • Ab Twister (crunch • Ab Doer (body bob) • Ab Rocker (oblique) oblique) and oblique) • SAM • Bent-knee sit-up • Ab Rocker (crunch • Ab Doer (body bob) • SAM and oblique) • Ab Doer (good morn- • Ab Roller (crunch and • Crunch (oblique) ing) oblique) • Bent-knee sit-up • Ab Roller (crunch and oblique) Least recruitment • Ab Twister (crunch • Crunch (normal) • Ab Twister (crunch • Ab Slide (straight and and oblique) • Ab Doer (good morn- and oblique) curved) • Ab Rocker (crunch ing, body boogie, and • Ab Rocker (crunch • Torso Track and oblique) body bob) and oblique) • Crunch (normal and • Ab Doer (good morn- • Ab Roller (crunch and oblique) ing, body boogie, and oblique) • Ab roller (crunch and body bob) • Bent-knee sit-up oblique) • Crunch (normal and oblique) • SAM • Ab Slide (straight and curved) • Torso Track54 J Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006
  11. 11. Biomechanical Differences Between the Crunch and Technique VariationsBent-Knee Sit-up Despite slightly greater external oblique EMG ac- tivities in oblique and curved techniques, mean It should be noted that not all abdominal exercises abdominal and oblique EMG activities generally wereinvolve the same degree of flexion of the lumbar not significantly different between technique varia-spine. Halpern and Bleck14 have demonstrated that tions for exercises such as the Ab Slide, crunch, Ablumbar spinal flexion was only 3° during the crunch Roller, Ab Twister, and Ab Rocker (eg, normalbut approximately 30° during the bent-knee sit-up. In crunch versus oblique crunch, straight Ab Slideaddition, the bent-knee sit-up has been shown to versus curved Ab Slide). Because simultaneous trunkgenerate greater intradiscal pressure18,19 and lumbar flexion and rotation have been shown to increase thecompression3 compared to exercises similar to the risk of torsional injury to the annulus fibrosis of thecrunch, largely due to increased lumbar flexion and intervertebral disk, as well as generate relatively highhip flexor activity. This implies the crunch may be a lumbar compressive forces,3 and because abdominalsafer exercise to perform than the bent-knee sit-up and oblique EMG activities were generally not differ-for individuals who need to minimize lumbar spinal ent between uniplanar and multiplanar trunk move-flexion or compressive forces due to lumbar pathol- ments, the additional risks involved when performingogy. multiplanar trunk flexion and rotation motions are Although the crunch and bent-knee sit-up were not warranted for individuals who have lumbar diskboth effective in recruiting abdominal musculature, pathologies.there were some differences. Several studies, includ-ing the current study, have shown that external Exercise Intensityoblique activity, and to a lesser extent internal ob- RESEARCHlique activity, are significantly greater in the bent- The Ab Slide and Ab Roller were the only 2knee sit-up compared to the crunch.1-3,16 However, commercial exercises in which resistance could notupper and lower rectus abdominis activities have be adjusted. This may account for more moderatebeen shown to be greater in the crunch compared to amounts of muscle activity in the Ab Roller (becausethe bent-knee sit-up.6,14 In addition, like the current resistance could not be added to make it harder) andstudy, hip flexor activity has been shown to be greater higher amounts of muscle activity in the Ab Slidein the bent-knee sit-up compared to the crunch.3,16 (because there was no way to make it easier). However, the Torso Track, which is performed in the REPORT same manner as the Ab Slide and did have resistanceThe Role of Abdominal Muscles in Trunk Stability bands that could be adjusted to make it easier or harder, had nearly identical muscle activity compared The role of the abdominal muscles, especially the to the Ab Slide. The subjects used in the currenttransverse abdominal and internal oblique, in en- study were all relatively young, active individuals whohancing spinal and pelvic stabilization and increasing all used the Torso Track in a more difficult resistanceintra-abdominal pressure (IAP) has been well studied, setting. This more difficult resistance may be appro-but still remains controversial.9,10,15,22,25 IAP has been priate for younger more active individuals, but older,shown to unload the spine by generating a trunk less active, or weaker individuals may not be able toextensor moment and tensile loading to the spine.11 correctly perform the Ab Slide due to its difficultyBy making the trunk a more solid cylinder by the IAP level. In addition, all subjects set the resistance formechanism, there is a reduction in spinal axial the Ab Doer, Ab Rocker, and Ab Twister to thecompression and shear loads. The attachments of the maximum number of resistance bands that could fittransverse abdominal and internal oblique into the on each device. Even with maximal resistance, these 3thoracolumbar fascia may enhance spinal and pelvic commercial abdominal devices recorded the loweststabilization, because when these muscles contract amount of abdominal activity. In contrast, the Abthey tense the thoracolumbar fascia. The transverse Slide, Ab Roller, and Torso Track generated signifi-abdominal, which is the deepest of the 4 abdominal cantly greater abdominal and oblique muscle activitymuscles, has been shown to exhibit a similar (within compared to the Ab Doer, Ab Rocker, and Ab Twister.15%) muscle activation pattern and amplitude as theinternal oblique muscle during many of the same Extraneous (Nonabdominal) Muscle Activitytrunk flexion movements (eg, bent-knee sit-up,crunch) used in the current study.16,17 The highest There are no studies that we are aware of that haveEMG activities from the internal oblique were for the reported extraneous muscle activity for abdominalAb Slide, Torso Track, crunch, and bent-knee sit-up machine exercises. Of the exercises tested, the Abexercises, which implies that these exercises may offer Slide and Torso Track produced the greatest activa-more effective stabilization to the spine and pelvis tion of the upper extremity musculature, includingcompared to the other exercises. the sternal pectoralis major, triceps brachii, andJ Orthop Sports Phys Ther • Volume 36 • Number 2 • February 2006 55

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